1. Field of the Invention
The present invention relates to a roll feed apparatus for feeding intermittently a sheet-like blank material to a processing station on a step-by-step basis. More particularly, the invention concerns a roll feed apparatus which includes a main roll and a subroll for feeding intermittently a strip-like sheet material to one or more work station such as metallic molds in a selective manner and which is suited to be intercorporated in an automated manufacturing machines or other machine tools.
2. Description of the Prior Art and Related Application
The hitherto known sheet material feeding apparatus of the type described above in which a combination of a one-way clutch and brake or a combination of a rotating cam and cam follower for converting a continuous rotation input to an intermittent rotation output for driving intermittently the feeding roller suffer from many shortcomings. For instance, it is difficult, not to say impossible, to feed a strip-like blank material stepwise by a predetermined quantity with a reasonable accuracy due to backlash in a gear train, a dimensional tolerance involved in implementing the cam and cam follower mechanism. The feeding operation may not be carried out at a high speed because jamming or deformation of the sheet material being stepwise fed will be then possibly involved. Troublesome and time consuming procedures are required for adjusting the feeding apparatus for different sheet materials having different thickness. Further, it has been impossible to vary a quantity of sheet material to be fed through a single feeding step in a stepless manner without interrupting operation of the feeding apparatus as well as associated tool or tools.
In order to obviate various troubles of the conventional apparatus, the present inventors have developed and proposed improved roll feed apparatus one of which is disclosed in Japanese Patent Application Laid-open No. 119642/80 published on Sept. 13, 1980 and corresponding to U.S. Pat. No. 4,304,348. This improved apparatus, however, is not completely satisfactory in that it cannot provide sufficiently high precision of operation particularly when the operation speed is high, although it can eliminate the above-described problems of the prior art.
The present inventors have worked out, through an intense study, a roll feed apparatus having a sector-shaped main roll, i.e. a main sector roll, and a sector-shaped subroll, i.e. a sub-sector roll, the main sector roll and the sub-sector roll being driven oscillatorily in such a manner that, when they rotate in one direction, they clamp the sheet therebetween and feed the same forwardly, while, when they rotate in the opposite direction, they release the sheet. This type of roll feed apparatus is shown in the specification of U.S. patent application Ser. No. 435,800. The use of the sector rolls decreases the inertia in the driving of the rolls and to enhance the precision of the feed of the sheet.
This roll feed apparatus incorporating sector gears, however, involves the following problems. Namely, the precision of the feed may be impaired undesirably due to the presence of a backlash in a pair of gears through which the rolls are connected drivingly. Antoher problem is that this apparatus necessitates an expensive and heavy coupling for moving two rolls towards and away from each other to effect the clamp and release of the sheet, while drivingly connecting two gears through a pair of gears mentioned above.